With micro-area X-ray fluorescence spectrometers that are used for performing component analysis on a micro-area of a specimen, X-rays that are emitted from an X-ray source must be focused to a very small diameter and irradiated onto the specimen. With the micro-area X-ray fluorescence spectrometer that is described in Non-Patent Literature 1, multi-capillary (the term used in the literature is “polycapillary” but the more commonly used term “multi-capillary” is used in this specification) X-ray lens is used.
The multi-capillary X-ray lens (“MCX”) is briefly explained next (see Patent Literature 1 and 2, etc.). FIG. 5 shows one mode of a MCX. FIG. 6 shows the principle behind the transmission of X-rays with a MCX. The basic construction of a MCX consists of numerous (approximately several hundred to a million) capillaries that are bundled together, each capillary being made of borosilicate glass and having a very small inner diameter in the range of approximately 2 μm to a dozen μm or so. As FIG. 6 shows, an X-ray beam that enters into a capillary 32 advances through the capillary while engaging in total reflection off the inner wall surface of the glass wall at an angle less than the critical angle. This principle is used to efficiently guide an X-ray. An X-ray can be efficiently guided whether the capillary 32 is linear-shaped such as that shown in FIG. 6(a) or bow-shaped such as that shown in FIG. 6(b).
There are many types of MCX. FIG. 5(a) shows a point/point type MCX 30 wherein X-rays that are emitted from an X-ray source that can be considered to be substantially a point are collected at the incident-side end face with a large solid angle and X-rays that are emitted from the emission-side end face on the opposite side is focused to a single point. With the MCX shown in FIG. 5(b), X-rays that are emitted from an X-ray source that similarly can be considered to be substantially a point are collected at the incident-side end face having a large solid angle and the X-rays are emitted as parallel beams from the emission-side end face. The MCX shown in FIG. 5(b) can also be a point/parallel type MCX 31 where the direction of travel is reversed.
Because, as afore-described, MCX is capable of collecting and guiding X-rays with a high efficiency, it is capable of irradiating a specimen with an X-ray having a high energy density and is therefore very effective in increasing the analysis sensitivity. On the other hand, it is not always very capable of focusing the X-rays, which have been collected with a high efficiency, onto a small irradiation area. One of the major reasons for this is that MCX, by its very principle of operation, causes blurring of the focal point. To explain, as shown in FIG. 7, because the X-ray travels through one capillary 32 while engaging in total reflection off the inner wall surface, the maximum reflection angle is the critical angle. For that reason, when the X-ray is emitted from the end face of capillary 32, the X-ray will have a divergence angle with respect to the optical axis (the center line of capillary 32) S with the maximum divergence angle being the critical angle θ. As a result, as shown in FIG. 8, the irradiation area of the X-ray that emerges from point-focus side end face 33 of MCX does not form an ideal point and instead forms an area 34 having a certain size.
Furthermore, even if the X-ray that emerges from the end face of a single-capillary 32 is made to be non-diverging, because of the limitations with the manufacturing of MCX, it is practically speaking impossible to cause all of the optical axes of a vast number of capillaries to perfectly focus to a single point. This factor also becomes a cause for the blurring of the focal point.
Because of the combination of such theoretical factors and the manufacturing limitations, the minimum focal point size of previous MCX has been limited to at most about 20 to 30 μm, and achieving any reduction in focal point size has been difficult. For example, with the device that is described in Non-Patent Literature 1, the size of the micro-area where the X-ray is irradiated is about 50 μm.
In recent years, there has been a strong need with analytic instruments such as micro-area X-ray fluorescence spectrometer and the like to perform measurements of components that are present in minute quantities in micro-areas. In response to such need, novel X-ray focusing devices that reduce the size of irradiation diameter of X-rays have been proposed. Patent Literature 3 combines MCX with a focusing member having a truncated cone shape, and Patent Literature 4 combines MCX with a Fresnel zone plate (FZP). Even though it is possible with these configurations to reduce the X-ray irradiation diameter to less than that achieved with MCX alone, the configuration of Patent Literature 3 has a tendency to reduce the intensity of the X-rays in the irradiated areas and is disadvantageous in terms of sensitivity, and the configuration of Patent Literature 4 has a cost disadvantage because of the very expensive cost of FZP required for obtaining a sufficient level of performance. So, both methods have their advantages and disadvantages.